Birdsong is not what you expect in an Olympic stadium. But that is what you hear if you enter the stadium where the handball and Taekwondo competitions are to be held in Athens this summer.

This stadium has a roof and therein lies the problem. Birds have found the rafters a delightful nesting place, and the stadium's acoustics amplify sound. Yet our guide seemed untroubled by the infestation. "They will go when we put the overhead lighting on for the Olympics," she said. But she failed to elaborate on whether the birds would simply take off, or be fried by the powerful lights.

Atos Origin, the Netherlands-based systems integrator for the Olympics, seems to be better prepared. Between now and the start of the games, the company responsible for making all the different IT systems work together, will test, test and test again.

There will be 200,000 hours of tests including a full technical rehearsal in mid-June simulating the busiest day of the games. A shadow IT team will try out disaster scenarios, from the possible, such as a massive hacker attack, to the improbable, such as Athens flooding in June.

Claude Philipps, the Frenchman who is chief integration manager for the Olympic project at Atos Origin, describes the pressures: "The biggest challenge is having an immovable deadline. I've worked on lots of large projects but you can usually go to the customer and say you will get your system later. With this project, the deadline is the deadline.

"Another challenge is the size of the team and the speed of the staff ramp-up in the final stages. We'll go from 100 staff on January 1 this year to 3,400 during the games. Of these, 400 will be from Atos Origin and 2,800 will be IT volunteers from Greece, with varying levels of IT expertise."

"At least 40 people on the project have worked with Olympic IT before [Atos acquisition SchlumbergerSema was involved in the winter Olympics in Salt Lake City], so they can act as mentors. We also provide five documents for new team members, checklists for their first day, and five trainers to make sure they are fully briefed on our policies and procedures, as well as on job-specific stuff."

The third challenge is working with so many third parties, suppliers of technology and other companies - like Atos itself - which are sponsoring the games. These include Swatch, which provides the athletes' times.

Security is also a challenge. Yan Noblot, information security manager at Atos Origin, says: "From our experience at Salt Lake City, we expect to get about 200,000 security alerts a day. This is too much information - at least 10 computer screens' worth. So we are using software to group similar attacks, and to highlight attacks from two different physical sites but the same computer address."

He is not being paranoid. At Salt Lake City someone managed to get into one of the computer rooms and install a wireless access point. They then tried to control the games systems from the outside, though this was soon detected and prevented.

Apart from keeping the computer infrastructure secure and running, Atos is also in charge of the games management system, which includes online accreditation for the athletes, volunteers and other members of the 200,000 strong Olympic "family". This has links to Greek police and immigration bodies, as a wrongly accredited person could be a security risk.

Information diffusion systems, especially getting results to the media, are also Atos' responsibility, including the press agency feed, the touch-screen commentators' information system, and the 2,500 kiosks in the Olympic village, which tell athletes where they need to be and when.

People have even tried to hack into the kiosks. Though you aren't meant to be able to use them to connect to the other internet sites or Olympic systems, that didn't stop people trying in Salt Lake City. "We had to secure at least 40 kiosks again at the end of every day," says Noblot.

"Our goal is for everything to be working so smoothly during the games that we will have nothing much to do on the day," says Philipps. "Boredom is good."

The line up

· The Olympic committee's IT budget is €350m-€400m

· There are 3,400 IT team members

· 28 sports (37 disciplines, 300 sports events)

· Around 60 venues (including 36 for competition)

· One 600,000sq ft PC "factory" for assembling PCs

· 10,500 computers

· 21,500 journalists needing information from IT systems

· One 24-hour command centre, with a back-up centre outside Athens

· 3-5 years planning for 16 days of games

· Joia Shillingford travelled as part of a group of UK press taken to Athens by Atos Origin